There is known an acoustic wave element having a piezoelectric substrate and an IDT (interdigital transducer) electrode (excitation electrode) provided on a major surface of the piezoelectric substrate (for example Patent Literature 1 or 2). The IDT electrode has a pair of comb-shaped electrodes. Each comb-shaped electrode has a bus bar which extends in a propagation direction of the SAW and a plurality of electrode fingers which extend from the bus bar in a direction perpendicular to the propagation direction of the SAW and which are arranged in the propagation direction of the SAW. Further, a pair of comb-shaped electrodes are arranged so that their plurality of electrode fingers mesh (intersect) with each other. Further, each comb-shaped electrode in Patent Literatures 1 and 2 has a dummy electrode which extends from the bus bar in the propagation direction of SAW and which has a front end facing the front end of an electrode finger of the other comb-shaped electrode with a gap interposed therebetween.
Patent Literature 1 discloses to widen the front end of the dummy electrode. In Patent Literature 1, it is considered that this configuration suppresses reflection and scattering of the SAW around the gap between the front end of the electrode finger and the front end of the dummy electrode and improves the resonance characteristic and filter characteristic of the acoustic wave element.
FIG. 15 in Patent Literature 2 discloses to connect the front end of the dummy electrode and the electrode finger which is adjacent to this dummy electrode in the propagation direction of the SAW. In Patent Literature 2, it is considered that this configuration lowers the sonic velocity in a region outside the cross range of the electrode fingers, shuts the SAW in the cross range, and improves the characteristics of the acoustic wave element.
However, in the art of Patent Literature 1, since the front end of the dummy electrode is widened, the gap between the front end of the dummy electrode and the front end of the electrode finger becomes smaller, so the chance of short-circuiting between these dummy electrode and electrode finger becomes higher. Further, the art of Patent Literature 2 does not take note of a propagation loss of the acoustic wave in the gap between the front end of the dummy electrode and the front end of the electrode finger and does not suitably suppress such propagation loss in the shape.
Accordingly, it is desired that there be provided an acoustic wave element and acoustic wave device which are capable of suppressing short-circuiting between a dummy electrode and an electrode finger while reducing the propagation loss of the acoustic wave.